Evapotranspiration of intercropping field in an artifical oasis in arid region

Data of a field experiment carried out at Zhangye Oasis, an arid region of northwest China, were used to evaluate the evapotranspiration during the 2004 growing seasons of an intercropping field of spring wheat and summer maize. The evapotranspiration was obtained mainly by two methods: Bowen ratio-energy balance(BREB) and reference crop evapotranspiration-crop coefficient (ET₀-K_c) method. The analysis results show that in a whole growing period, the total ET is 688 mm and a daily mean 3.4 mm/d by BREB, while a total of 666 mm and a daily mean 3.3 mm/d by ET₀-K_c. A close result (733 mm) is also obtained by Soil Water Balance(SWB) method. Using the results of BREB, some conclusions are drawn as follows. The ET varies with growing stages. At initial growing stage, middle growing stage and the end growing stage, the ET values are 1.19 mm/d, 4.41 mm/d and 2.58 mm/d, and with the percentages of total ET of 7.79%, 78.73% and 13.48%, respectively. In March, ET maintains in a lower level. In April and May, the ET increases sharply. It reaches the maximal value in June. After that, it decreases lightly and gradually in July and August. With the ending of growing, the ET decreases rapidly in September. Hourly ET analysis shows that at 7∶00～8∶00 a.m., the evapotranspiration begins, at 14∶00 it reaches maximal value and at 19∶00～20∶00 p.m., the evapotranspiration stops. The hourly intensity of ET at different stages varies greatly.